CO2/O2 incubator predictive failure for CO2 and O2 sensors

ABSTRACT

Methods and apparatus for a predictive warning system of the failure of O 2  and CO 2  sensors, which are particularly suited for an incubator environment are disclosed. An application of the predictive failure of O 2  and CO 2  sensor method and apparatus to incubators is also disclosed.

FIELD OF THE INVENTION

[0001] The present invention relates generally to the prediction offailure of sensors within a controlled gas atmosphere enclosure. Moreparticularly the present invention concerns methods and apparatus forthe prediction of failure of O₂ and CO₂ sensors within an incubatorenvironment.

BACKGROUND OF THE INVENTION

[0002] There are a number of commercial applications for controlled gasatmosphere enclosures including incubators. For example, electricalcomponents and circuits are often tested in enclosures at a selectedtemperature and/or relative humidity for a period of time. Anothercommon application for controlled atmosphere enclosures is the growth ofbiological cultures in a laboratory. As will be discussed herein withregard to a particular embodiment, the present invention may beadvantageously employed in connection with a controlled gas atmosphereincubator in which a chamber for biological cultures is heated and inwhich the atmosphere of the chamber is controlled as to one or moreconstituent gases and/or the relative humidity.

[0003] A typical enclosure of the foregoing type includes a generallycubical outer housing made up of five insulated walls (top, bottom, leftside, right side, and rear) and an insulated front door. The door ismounted on hinges on the front of one of the side walls and may beopened to permit access to the interior of the incubator. When the dooris closed, it is suitably sealed about its periphery to the housingwalls to form the sixth wall of the housing. The incubator chamber, inwhich biological cultures are grown, is formed by inner walls, insidethe insulated outer walls, and typically includes shelves upon whichculture containers are placed. The shelves are carried by suitable shelfsupports inside the chamber.

[0004] Most incubators of this type are either water jacket incubatorsor forced draft incubators. In a water jacket incubator the innerchamber is heated to the desired temperature by a sealed jacket of watersurrounding the five fixed sides of the incubator chamber. The waterjacket lies between the chamber wall and the insulated housing walls andis heated by heating elements in thermal contact with the water in thewater jacket. Due to the thermal conductivity of water, the heat fromthe individual heating elements is relatively evenly dispersed throughthe water in the water jacket, providing even heating of the chamber.Such even heating is desirable in order to provide a uniform temperaturefor the biological cultures in different areas within the chamber and inorder to prevent “cold spots” on the inner chamber wall upon whichcondensation can form.

[0005] Although the heating of the chamber walls in a water jacketincubator is substantially uniform, the chamber atmosphere will stratifythermally if the chamber atmosphere is undisturbed. When suchstratification occurs, the temperature of the chamber atmosphere isgreater at the top of the chamber than at the bottom of the chamber. Inaddition, if a constituent gas concentration is maintained in thechamber, such as a particular CO₂ level, the constituent gas will alsostratify within the chamber atmosphere. Consequently, it is desirable tomaintain a certain rate of flow of gas within the chamber to assureuniformity of temperature and of constituent gases. In order to do this,typically a portion of the chamber is separated from the main chamberarea by a wall to define a duct extending, for example, along a side ofthe chamber. A small blower or fan is placed in the duct and the chamberatmosphere is circulated, such as from a duct inlet in the upper portionof the chamber to a duct outlet in a lower portion of the chamber.

[0006] In a forced draft incubator, the inner chamber walls areinsulated from the outer housing walls by a layer of insulation insidethe housing walls. However, in this case there is no water jacketinterposed between the insulated outer walls and the inner chamberwalls. To obtain heating of the chamber in a forced draft incubator,some type of duct, such as described above, is typically provided withinthe chamber, and a fan and a heating element are mounted in the duct. Asthe fan circulates air from the main chamber area through the duct, thecirculated chamber atmosphere is heated by the heating element. In orderto heat the chamber atmosphere substantially uniformly, and to thedesired temperature, considerably greater air flow is required than inthe case of a water jacket incubator.

[0007] In a typical forced draft incubator, or water jacket incubator,if a constituent gas in the atmosphere of the incubator chamber is to bemaintained at a particular level, a probe is introduced into thechamber, perhaps within the duct through which the chamber atmospherecirculates. In the case of CO₂, for example, a CO₂ sensor is introducedinto the incubator chamber to measure the concentration of CO₂ therein.A source of CO₂ is then coupled to the interior of the chamber through acontrolled valve, with an automatic control system actuating the valveas required to maintain the CO₂ concentration in the chamber at aselected level.

[0008] The humidity in a forced draft incubator is also oftencontrolled. Rather than introducing steam or water into the incubatorchamber as may be done in the case of a water jacket incubator, in aforced draft incubator quite often a pan of water is placed upon thefloor of the incubator chamber, and the recirculated chamber atmosphereis directed out of the bottom of a duct across the surface of the waterin the pan. Due to the higher recirculation rates in a forced draftincubator, appropriate humidification of the chamber is obtained.

[0009] In either a forced draft or a water jacket incubator, sensorssuch as for CO₂ or humidity have typically been located within thechamber atmosphere itself, although perhaps within a recirculation duct,as earlier described. Such sensors in the chamber are subject to thechamber atmosphere, and a sensor can fail or suffer performancedegradations due to contaminants or the accumulation of a coating on thesensor. The presence of such sensors in the incubator chamber itselfalso makes cleaning of the chamber interior more difficult. In fact, thevery existence of a duct or the like for the circulation of the chamberatmosphere within the chamber introduces difficulties in cleaning thechamber.

[0010] The recirculation of the chamber atmosphere, such as through aduct, in either type of incubator presents yet another problem, that ofpotential contamination of biological cultures within the chamber.Contaminants such as mold spores are almost invariably present in thechamber atmosphere and may be directed by the recirculatory air flowinto the biological culture containers. Culture contamination problemsare exacerbated by the higher air flows required in forced draftincubators.

[0011] Higher air flow rates involved in forced draft incubators have afurther disadvantage in that the higher flow rates tend to dry outbiological culture media. To a large degree, the necessity of offsettingthis desiccation results in the requirement for humidity control inforced draft incubators. In such incubators, a relatively high humidityis maintained so that the drying effect of the gas flow is ameliorated.

[0012] Furthermore, a well known problem with incubator systems is thatit is difficult to know when a pending failure of the O₂ and CO₂ sensorsmay occur. Incubators are typically used for growing cultures in acontrolled environment wherein both temperature and atmospheric gasconcentration are maintained at selected levels. For certainapplications it is highly desirable to have both temperature and gasconcentrations maintained within strict tolerances while still allowingeasy access to the incubator chamber for adding or removing items to andfrom the chamber or for inspecting the contents of the chamber. Controlof environmental variables is desirable to maintain accuracy andreproducability of incubation results.

[0013] Therefore, it would be desirable to provide an incubator havingthe ability to provide a warning of a pending failure of the O₂ and CO₂sensors mounted therein.

SUMMARY OF THE INVENTION

[0014] The foregoing needs have been satisfied to a great extent by thepresent invention wherein, this invention includes the formulation ofalgorithms utilized for early warning of O₂ and/or CO₂ sensors. Thealgorithms are included in the firmware for an embedded controller andoperate to analyze the sensors for lifetime adjustment every hour asdetermined by the cumulative clock within the controller. As an hourroll-over occurs, the sensor lifetime value is adjusted and normalizedto an hour count stored in %O₂ lifetime hours used at 20° C. Thenormalization includes assumptions that the O₂ concentration and the O₂sensor temperature remained constant over the previous hour.

[0015] It is accordingly an object of the present invention to provide apredictive warning system of pending sensor life failure.

[0016] There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended hereto.

[0017] In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract, are for the purpose ofdescription and should not be regarded as limiting.

[0018] As such, those skilled in the art will appreciate that theconception upon which this disclosure is based may readily be utilizedas a basis for the designing of other structures, methods and systemsfor carrying out the several purposes of the present invention. It isimportant, therefore, that the claims be regarded as including suchequivalent constructions insofar as they do not depart from the spiritand scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a block diagram of a preferred embodiment of the presentinvention showing a microcontrolled system with O₂ and CO₂ sensors, anembedded controller and a power board.

[0020]FIG. 2 shows a user interface indicating the variables oftemperature, CO₂ and O₂ in an incubator environment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0021] Referring now to the figures, FIG. 1 illustrates amicrocontroller based system 10, an embedded controller 20, O₂ sensor25, CO₂ sensor 35, and a power board 30 which are set in an incubatorcabinet 40. This microcontroller based system 10 has the ability totrack the O₂ and the CO₂ set point, in percentage, along with theoperation time. O₂ sensor 25 may be specified to perform for 900,000 O₂percentage hours. Thus, it is a straightforward calculation to determinehow close the system is Coming to 900,000 O₂ percentage hours. In thecase of a CO₂ sensor 35, for example, the CO₂ sensor 35 can beintroduced into the incubator cabinet 40 to measure the concentration ofCO₂ present therein. A source of CO₂ (not shown) is then coupled to theinterior of the incubator cabinet 40 through a controlled valve (notshown), with an automatic control system (not shown) which may includethe embedded controller 20 actuating the valve as required to maintainthe CO₂ concentration in the incubator cabinet 40.

[0022] Such sensors as the O₂ sensor 25 and CO₂ sensor 35 in anincubator cabinet 40 may be subject to the incubator cabinet 40 internalatmosphere, and these sensors can fail or suffer performancedegradations due to contaminants or the accumulation of a coating on thesensor over time.

[0023] Referring to FIG. 2, it would be highly beneficial to the user tobe forewarned of this pending threshold. For instance, at somepredetermined value, say 800,000 O₂ percentage hours, the user wouldbegin to see a warning on interface display 50, such as “Replace O₂sensor, P/N XXXXXX.”

[0024] A similar scenario holds true for CO₂ sensor 35 with respect topercentage hours and lifetime use. The main difference between CO₂sensor 35 from the O₂ sensor 25 is that the operational life would bebased on the warranty period of the CO₂ sensor 35: the time that it isguaranteed to operate correctly by the manufacturer. Again, the systemis capable of tracking the operation time of CO₂ sensor 35 as well.

[0025] Similar interface display 50 notices will also be provided forre-calibration times for both sensors.

[0026] O₂ Sensor Life Detailed Example

[0027] The O₂ sensor lifetime is dependent on two variables, temperatureand O₂ concentration. Interfacing an O₂ sensor 25 to an embeddedcontroller 20 designed to control temperature and O₂ (among otherparameters) as aforementioned allows the lifetime usage of the sensor tobe monitored and ultimately can warn a user of impending sensorreplacement. The preferred embodiment analyzes the sensor for lifetimeadjustment every hour as determined by the cumulative clock within thecontroller 20. As the hour roll-over occurs, the sensor lifetime valueis adjusted and normalized to an hour count stored in %O₂ lifetime hoursused at 20° C. The normalization includes assumptions that the O₂concentration and the O₂ sensor temperature remained constant over theprevious hour. Although this assumption may at first appear invalid, 1)an incubator application typically holds parameters constant for longperiods of time, 2) it is easily adapted to a different application, and3) the O₂ sensor life hours count is a large number (thus if smallnumbers of the hour roll-overs are inaccurate it will not effect thefinal result). The following code snippet is an excerpt from thefirmware in the embedded controller 20 that executes every hour toincrease the O₂ sensor lifetime:

[0028] Code Snippet (executes every hour):

[0029]O2SensorLifeUsed20C=+=(float)(((float)(O2Act/10.0))*((float)(100.0/(1192.0/(exp(2.0+(0.0239*(Temp/10.0))))))));

[0030] O2Act=10*percentage O2

[0031] Temp=10*temperature (° C.).

[0032] Examples:

[0033] O2Act=250 (25% O₂)

[0034] Temp=370 (37.0° C.)

[0035] O2SensorLifeUsed+=37.523

[0036] Therefore, for this particular hour adjustment the sensor lifeutilized over the last hour was 37.523 for the sensor at 25% O₂ and37.0° C. It should be noted that the transfer function above may bedifferent for other O₂ sensors 25 and that the preferred embodimentutilizes self-powered, diffusion limited, metal-air battery types.

[0037] At this point the embedded code could compare the variableO2SensorLifeUsed20C. with another variable that represents the total %O₂lifetime hours used at 20° C. When the O2SensorLifeUsed20C is greaterthan the %O₂, it is time to replace the sensor and the system canrespond through the interface display 50.

[0038] In an actual application, the number may be padded to allow fortime for the user of the device to receive a warning prior toexpiration. Furthermore, the embedded user interface display 50 shouldallow a reset interface 60 to re-zero the count for in the field sensorreplacement.

[0039] The above description and drawings are only illustrative ofpreferred embodiments which achieve the objects, features, andadvantages of the present invention, and it is not intended that thepresent invention be limited thereto. Any modification of the presentinvention which comes within the spirit and scope of the followingclaims is considered to be part of the present invention.

What is claimed is:
 1. A method of predicting failure of gas sensors inan incubator environment comprising the steps of: analyzing at least onegas sensor for lifetime adjustment; adjusting a percentage gas sensorlifetime hours; normalizing said lifetime hours adjustments; calculatingthe percentage gas sensor lifetime hours for comparison with itsrespective maximum percentage hours for said gas sensor; and displayinga warning message to a user.
 2. The method of claim 1, furthercomprising repeating the adjusting step every hour as determined by acumulative clock in an embedded controller.
 3. The method of claim 2,wherein an hour count is stored in percentage gas sensor lifetime hoursat a temperature of 20 degrees Celsius in said embedded controller. 4.The method of claim 3, wherein the step of normalization includes gasconcentration and gas sensor temperature remaining constant over aprevious hour.
 5. The method of claim 3, wherein the embedded controllertracks O₂ and CO₂ set points by percentage.
 6. The method of claim 1,wherein the step of displaying a warning message to a user occurs oncethe percentage gas sensor lifetime hours exceed 90% of said respectivemaximum percentage hours for said gas sensor.
 7. The method of claim 3,wherein the embedded controller tracks O₂ and CO₂ operation times. 8.The method of claim 4, wherein said gas sensor is an O₂ sensor.
 9. Themethod of claim 4, wherein said gas sensor is a CO₂ sensor
 10. Apredictive warning system for incubator gas sensor failure, comprising:at least one gas sensor disposed in an incubator housing; an embeddedcontroller for analyzing the at least one gas sensor for failure; and aninterface display for indicating said gas sensor failure to a user. 11.The predictive warning system of claim 10, wherein said embeddedcontroller tracks the O₂ and CO₂ set points by percentage.
 12. Thepredictive warning system of claim 10, wherein said interface display isresettable.
 13. The predictive warning system of claim 10, wherein saidembedded controller tracks the O₂ and CO₂ operation times.
 14. Thepredictive warning system of claim 10, wherein said embedded controlleradjusts a percentage gas sensor lifetime hours every hour.
 15. Thepredictive warning system of claim 14, wherein said interface displayindicates a warning message to said user once the percentage gas sensorlifetime hours exceed 90% of their respective maximum percentage hoursfor said gas sensor.
 16. The predictive warning system of claim 15,wherein said gas sensor is an O₂ sensor.
 17. The predictive warningsystem of claim 15, wherein said gas sensor is a CO₂ sensor.
 18. Apredictive warning system for incubator gas sensor failure, comprising:means for analyzing at least one gas sensor for lifetime adjustment;means for adjusting a percentage gas sensor lifetime; means fornormalizing said lifetime hours adjustments; means for calculating thepercentage gas sensor lifetime for comparison with their respectivemaximum percentage hours for said gas sensor; and means for displaying awarning message to a user once the percentage gas sensor lifetime hoursexceed 90% of said respective maximum percentage hours for said gassensor.
 19. The predictive warning system of claim 18, furthercomprising: means for adjusting the percentage gas sensor lifetime hoursevery hour.
 20. The predictive warning system of claim 19, wherein anhour count is stored in percentage gas sensor lifetime hours at atemperature of 20 degrees Celsius in said embedded controller.
 21. Thepredictive warning system of claim 19, wherein the step of normalizationincludes gas concentration and gas sensor temperature remaining constantover a previous hour.
 22. The predictive warning system of claim 19,wherein the embedded controller tracks O₂ and CO₂ set points bypercentage.
 23. The predictive warning system of claim 19, wherein theembedded controller tracks O₂ and CO₂ operation times.
 24. Thepredictive warning system of claim 18, wherein said means for displayinga warning message to a user is resettable.
 25. The predictive warningsystem of claim 20, wherein said gas sensor is an O₂ sensor.
 26. Thepredictive warning system of claim 20, wherein said gas sensor is an CO₂sensor.